The present invention relates to an amplifier circuit capable of preventing the occurrence of transient noise such as pop noise caused at the time when a power source switch or muting switch is turned on and off.
Direct-current blocking capacitors are usually employed at various locations in amplifiers for tape recorders and the like. These capacitors form various time constant circuits in combination with resistors and the like which form the amplifier. Such time constants are usually different from one another. Therefore, unpleasant noise is caused at the transient time period during which the power source is turned on and the amplifier circuit attains to its normal operation point. This noise is known as so-called pop noise. Noise of this type can be practically eliminated by a specially-designed DC amplifier using positive and negative dual power sources, or a muting relay. However, in the case of a portable tape recorder driven by a battery, AC amplifiers of the single power source type are common. AC amplifiers of this type cause pop noise every time the power source is turned on and off. Noise of this type is also caused when muting operation is intended, by changing the bias potential which determines the operation point of amplifier.